cap_prctl - Linux

Overview

cap_prctl is a command-line utility in Linux that allows users with CAP_SETPCAP privilege to manipulate the capabilities of the current process or threads. It is used to change the effective and inherited capabilities of the process, enabling fine-grained control over the permissions granted to specific programs.

Syntax

cap_prctl [ACTION] [CAPABILITY] [THREAD_FLAG] [PID]

where:

• ACTION specifies the operation to perform.
• CAPABILITY is the capability to be modified.
• THREAD_FLAG applies the changes only to specific threads.
• PID is the process ID (optional).

Options/Flags

• -a (ACTION): Add the capability to the set.
• -d (ACTION): Drop the capability from the set.
• -l (ACTION): List the effective and inheritable capabilities of the process.
• -r (THREAD_FLAG): Apply to all threads of the process.
• -e (THREAD_FLAG): Apply only to the calling thread.
• -p (THREAD_FLAG): Specify the PID of the thread to affect.

Examples

• Add CAP_SYS_ADMIN to the process:

cap_prctl -a CAP_SYS_ADMIN

• List the effective capabilities of the process:

cap_prctl -l

• Drop CAP_DAC_READ_SEARCH from all threads:

cap_prctl -dr CAP_DAC_READ_SEARCH -r

• Apply capabilities to a specific thread of another process:

cap_prctl -a CAP_NET_ADMIN -p 1234

Common Issues

• Permission Denied: The user must have CAP_SETPCAP privilege to use cap_prctl.
• Invalid Capability: The specified capability is not a valid capability.
• Invalid Thread: The specified thread does not exist.

Integration

cap_prctl can be integrated with other commands to perform advanced tasks:

• setuid with capabilities: Create a program with reduced privileges that elevates to a specific set of capabilities when needed.
• Container Security: Set specific capabilities for containers to restrict their actions and enhance security.
• SELinux: Modify capabilities in SELinux environments to define fine-grained access controls.

Related Commands

• capabilities
• lscap
• setcap